Nanostructured transition metal, alloy or composite are of technical importance as homogeneous or heterogeneous chemical catalysts. Nanocomposite comprises small particles typically having diameters less than 100 nm on the surface of a supported material for various chemical uses. Precious metal alloy nanocomposites are of special importance for their catalytic applications include photovoltaics, supercapacitors, batteries, fuel cells, and materials for hydrogen storage. Precious metals within the platinum group such as platinum, palladium, ruthenium and rhodium are well known for their catalytic capabilities in bulk and deposited phases. Such catalytic materials can be fabricated through bulk metal processes or through nanoparticle synthesis. Platinum group metals are very expensive metals and hence the catalysts are invariably expensive and are often designed to minimize the amount of metal used rather than to optimize performance. In addition, platinum group catalysts are prone to being “poisoned” in the presence of carbon monoxide and hence limit the application. Electrocatalyst made with cheaper and abundant transition metals that offer excellent performance will be desirable for industrial application.
Available preparation methods for catalytic transition metal alloy include sputtering, chemical reduction, inert gas evaporation, thermal decomposition and physical vapor deposition. These methods are complicated and demanding sophisticated instrumentation. In addition, they also suffer from contamination from mechanical parts, from reaction byproducts, agglomeration and difficulty in scalability.
For the fuel cell application, high-surface-area carbon blacks and often used to serve as effective solid supports to disperse nanoscale noble metal and to electrocatalyze oxidation and reduction reactions within the cells. Despite the high surface area of the conducting carbon support and effective dispersion of the electrocatalyst, self-agglomeration of the particle within the electrode structure limits the approach of the reactants to the active sites, and as a result, not all of the electrocatalyst in the electrode can be accessed.
Significant needs remain for synthesizing well-defined, non-agglomerated electrocatalyst of controlled size and composition.